The present invention relates to a ranging system, a transmitting terminal, a receiving terminal, a ranging method, and a computer program for use with a multi-carrier transmission system.
It is common knowledge that a plurality of computers are connected by suitable telecommunication means to constitute a wireless local area network (LAN) over which files and data are exchanged and shared wirelessly.
For wireless LANs setups, there exist a number of standards, notably IEEE 802.11a. The IEEE 802.11a standard supports the 5-GHz OFDM modulation method that provides communication speeds of up to 54 Mbps. According to the standard, wireless communications are conducted using 52 subcarriers.
There exist ranging systems developed to measure distances between devices using a wireless LAN subject to the IEEE 802.11a standard or the like. To measure the distance between a transmitting and a receiving terminal on the wireless LAN requires that each terminal first determine the positions where packets are received.
Determining where packets are received over the wireless LAN illustratively under the IEEE 802.11a may involve determining the packet-receiving positions in terms of synchronizing positions. For example, suppose that following the operation of an AD converter in the receiving terminal, a digital circuit in the receiving terminal operates at a clock speed of 80 MHz.
Suppose also that the received packets are each headed by a known signal sequence. After the processing by the AD converter of the receiving terminal, the known signal is used to calculate correlations with the received signals. Because the correlations tend to become large in the positions of the known signal embedded in the packets, a search for a peak of the correlations makes it possible to determine where each packet was received. This in turn allows the distance between the terminals to be measured.
Meanwhile, in a field quite different from the ranging over wireless LANs, there exists the so-called MUSIC algorithm, a spectrum estimation algorithm for use in analyzing signal propagations based on adaptive arrays. This technique is discussed illustratively in “Adaptive Signal Processing by Use of Array Antennas” by Nobuyoshi Kikuma (published in Japanese from Science Press, Inc. on Sep. 20, 1998; pp. 191-203).